The invention relates to improvements in piston engines (also known as reciprocating or displacement engines), and more particularly to improvements in methods of and means for preventing or reducing the extent and/or frequency of stray movements of crankshafts in such engines. Still more particularly, the invention relates to improvements in the construction and mounting of vibration dampers for the crankshafts of piston engines.
Published German patent application Serial No. 195 19 261 discloses a torsional vibration damper which comprises an annular casing adapted to be connected to the shaft of a machine and confining a flywheel which is rotatable relative to the casing against the opposition of a body of viscous fluid. This published application proposes to position the casing of the vibration damper at the front end face of, and to fasten the casing to, the front end (snout) of the crankshaft. A drawback of such proposal is that the thus attached damper occupies a substantial amount of space which is not always available under the hoods of certain types of motor vehicles (such as compact cars), especially if the engine is installed transversely of the direction of forward movement of the conveyance.
Published German patent application Serial No. 40 25 848 discloses a modified vibration damper which is intended for use in piston engines and employs annular flywheels as well as a hub which is to be secured to the crankshaft of the engine. The annular flywheels are movably secured to the hub by buffers of rubber or other suitable elastomeric material. The hub is provided with or carries a pulley for one or more endless belts serving to transmit motion to the crankshaft of the engine and/or to one or more auxiliary aggregates of the motor vehicle.
One of the purposes of vibration dampers for the crankshafts of piston engines is to suppress the characteristic frequencies (harmonic vibrations) of the crankshafts. In many instances, the characteristic frequency of the crankshaft in the housing of a piston engine is in the range of between 300 and 450 Hz. Such frequency is induced primarily as a result of regularities attributable to compression and expansion that take place in the cylinders for the pistons of the engine. Vibrations at the torsional resonancy can result in breakage of the crankshaft, and this is the reason that the crankshafts of piston engines are normally equipped with vibration dampers (e.g., in the form of heavy, rubber-mounted wheels in front of the crankshaft) to counter harmonic vibrations.
In order to achieve a satisfactory vibration damping action, the vibration damping frequency must be selected with a rather high degree of accuracy. As already mentioned above, presently known attempts at adequate damping of vibrations of a crankshaft in a piston engine include the provision of at least one annular flywheel which is movably connected to a hub or another input element of the vibration damper by a buffer of rubber (or other energy-storing elastomeric material), or by a body of oil or another suitable viscous fluid.
In addition to their often excessive space requirements, the aforediscussed presently known vibration dampers for the crankshafts of piston engines exhibit the drawback that the viscosity of fluid can be greatly influenced by changes of temperature and that such temperature changes can also exert an undue influence upon the spring gradient of the elastomeric material. It is to be borne in mind that a vibration damper for the crankshaft of a piston engine is installed in immediate or very close proximity to one or more sources of pronounced heat. Attempts to overcome or to reduce the undesirable influence of elevated temperatures upon the predictability and reliability of operation of conventional vibration dampers for crankshafts include the utilization of oversized vibration damping masses to thus widen the frequency range within which the damper is or should be effective. However, the utilization of oversized masses brings about other serious problems and drawbacks such as a greatly increased fuel consumption and an increased resistance of rotary components of the piston engine to the setting in rotary motion.